Add clarification text to browsers file
Add clarification text to browsers file

CLOSES: DOC-1240
flag=none

Test plan:
- jenkins passes

Change-Id: I1997e5c755d5277e7cb901102c1237ff74eeffe9
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/246947
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
QA-Review: Erin Hallmark <2a4b17b11682b229726079a631360cf016a43450@instructure.com>
Product-Review: Erin Hallmark <2a4b17b11682b229726079a631360cf016a43450@instructure.com>

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