Include Overleaf in science track description.
Include Overleaf in science track description.

This PR updates the Science Track page to include some notes about Overleaf joining us and the Sprint day.

Hopefully @johnhammersley can have a look at this before we merge.
wjt/pyconuk.org,jneves/pyconuk.org,sparkslabs/pyconuk.org,jvlomax/pyconuk.github.io,grimpunch/pyconuk.org,evildmp/pyconuk.org,Avaren/pyconuk.org,1stvamp/pyconuk.org,grimpunch/pyconuk.org,PyconUK/pyconuk.org,Avaren/pyconuk.org,PyconUK/2015.pyconuk.org,BjarniRunar/pyconuk.org,VishvajitP/pyconuk.org,ntoll/pyconuk.org,PyconUK/pyconuk.org,jvlomax/pyconuk.github.io,grimpunch/pyconuk.org,lordmauve/pyconuk.org,moreati/pyconuk.org,PyconUK/2015.pyconuk.org,BjarniRunar/pyconuk.org,snim2/pyconuk.org,jneves/pyconuk.org,moreati/pyconuk.org,PyconUK/pyconuk.org,sixty-north/pyconuk.org,jvlomax/pyconuk.github.io,jrobinson-uk/pyconuk.org,jamesbroadhead/pyconuk.org,jrobinson-uk/pyconuk.org,evildmp/pyconuk.org,mojones/pyconuk.org,jamesbroadhead/pyconuk.org,zeth/pyconuk.org,sparkslabs/pyconuk.org,snim2/pyconuk.org,helenst/pyconuk.org,mojones/pyconuk.org,jvlomax/pyconuk.org,oinopion/pyconuk.org,sixty-north/pyconuk.org,zeth/pyconuk.org,moreati/pyconuk.org,Avaren/pyconuk.org,evildmp/pyconuk.org,jamesbroadhead/pyconuk.org,snim2/pyconuk.org,jrobinson-uk/pyconuk.org,sixty-north/pyconuk.org,jneves/pyconuk.org,tomviner/pyconuk.org,nanuxbe/pyconuk.org,wjt/pyconuk.org,jvlomax/pyconuk.org,zeth/pyconuk.org,lordmauve/pyconuk.org,VishvajitP/pyconuk.org,wjt/pyconuk.org,helenst/pyconuk.org,helenst/pyconuk.org,BjarniRunar/pyconuk.org,nanuxbe/pyconuk.org,ntoll/pyconuk.org,mojones/pyconuk.org,PyconUK/2015.pyconuk.org,tomviner/pyconuk.org,oinopion/pyconuk.org,1stvamp/pyconuk.org,tomviner/pyconuk.org,VishvajitP/pyconuk.org